1. Field of the Invention
The present invention relates to a vibration element in which a piezoelectric element is fixed onto a substrate, a manufacturing method thereof, and a vibration wave actuator using the vibration element.
2. Description of the Related Art
In a vibration wave actuator, a piezoelectric element has commonly been used as a vibration source of a vibration element. A single plate piezoelectric element, or a laminated piezoelectric element obtained by stacking many piezoelectric layers and then sintering formed/integrated layers, is used as the piezoelectric element. Particularly, compared with the single plate piezoelectric element, the laminated piezoelectric element has an advantage of being able to obtain a large deformation or a large force with a low applied voltage due to multi-layering (U.S. Pat. No. 7,109,639).
FIG. 5 is a perspective view of appearance of a linear vibration wave (ultrasonic wave) actuator 30 discussed in U.S. Pat. No. 7,109,639. The linear vibration wave actuator 30 includes a vibration element 31 and a rod-shaped moving member (linear slider) 36 in pressure contact. The vibration element 31 includes a laminated piezoelectric element 35 and a drive plate 32 and the laminated piezoelectric element 35 has a plurality of piezoelectric layers and electrode layers stacked alternately. The drive plate 32 is made of metal and is bonded to the laminated piezoelectric element 35 by an adhesive. The drive plate 32 includes a plate portion formed in a rectangular shape and two protruding portions 33a and 33b formed in a convex shape on a top surface of the plate portion. The protruding portions 33a and 33b have contact portions 34a and 34b, respectively, formed on a tip surface thereof. The contact portions 34a and 34b are members to come directly into contact with the linear slider 36 as driven elements and thus have predetermined wear resistance. The linear vibration wave actuator 30 excites two bending vibration modes to cause the protruding portions 33a and 33b to make an elliptic motion. The elliptic motion generates a relative movement force between the linear slider 36 and the vibration element 31, with which the linear slider 36 is in contact under pressure. The linear slider 36 is linearly driven by the relative movement force.
When the laminated piezoelectric element 35 is manufactured, first a green sheet to be a piezoelectric layer is produced from piezoelectric material powder and an organic binder by the doctor blade or a similar method and then an electrode material paste is printed to predetermined positions on the green sheet to produce an electrode layer. Then, a predetermined number of green sheets are stacked in a plane shape and pressurized for lamination. Subsequently, the piezoelectric layer and the electrode layer are sintered at the same time to integrate the layers, and polarization is performed to finish the laminated piezoelectric element 35 to predetermined dimensions by machining in the end. Also a piezoelectric electrostrictive film actuator having an integrated laminated structure integrated by heat treatment of an electrode material and a piezoelectric material alternately stacked in a layered shape on at least one side of the ceramic substrate is known.
FIGS. 6A and 6B illustrate a vibration element 40 integrated by sintering a piezoelectric element 41, including a piezoelectric layer 45 and electrode layers 44 and 46, and a ceramic substrate 42, as a vibration element, at the same time.
A piezoelectric layer 43 as a compound layer having the same components or the same main components as the piezoelectric layer 45 is placed between the electrode layer 44 of the piezoelectric element 41 and the ceramic substrate 42, and the piezoelectric element 41 and the ceramic substrate 42 are joined by sintering (Japanese Patent Application Laid-Open No. 2009-124791).
In the vibration element 31 of the linear vibration wave actuator 30 discussed in U.S. Pat. No. 7,109,639, the laminated piezoelectric element 35 and the drive plate 32 made of metal are bonded by an adhesive made of resin.
However, an adhesive made of resin is relatively soft. Thus, vibration damping of a vibration element is large and particularly an influence of the vibration damping of a vibration element increases with a decreasing size thereof, causing degradation of efficiency of a small vibration wave actuator as a leading factor. Moreover, when the vibration element is miniaturized, an influence of variations in thickness of an adhesion layer and accuracy of position due to adhesion on performance of a small vibration wave actuator increases and also variations of performance of small vibration wave actuators increase.
Further, according to the manufacturing method of a conventional laminated piezoelectric element, the costs of plant and equipment investment of production units for green sheet formation from piezoelectric material powder, laminating press, machining and the like are large, contributing to increasing manufacturing costs as a factor. Thus, like the above piezoelectric electrostrictive film actuator having an integrated laminated structure, a method of directly fixing a laminated piezoelectric element to a ceramic substrate without providing an adhesion layer with an adhesive at the same time as the production of the laminated piezoelectric element is used.
However, a chemical reaction is normally less likely to occur between an electrode layer of a piezoelectric element and a ceramic substrate, resulting in comparatively low bonding strength between the electrode layer and the substrate. Thus, the element may peel off from the substrate from the start or is more likely to peel off due to vibration.
Therefore, Japanese Patent Application Laid-Open No. 2009-124791 proposes the vibration element 40 integrated by sintering after the piezoelectric layer 43 being placed between the electrode layer 44 of the piezoelectric element 41 and the ceramic substrate 42.
However, while it is possible to increase bonding power with the ceramic substrate 42 by placing the piezoelectric layer 43 therebetween, the piezoelectric element 41 may peel off from the ceramic substrate 42 if a larger vibration amplitude is provided to a vibration element. Thus, it becomes necessary to further increase bonding power between the piezoelectric element 41 and the ceramic substrate 42.